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Oct. 14 1952 BAKKER TRUNK CIRCUIT REPEATER Original Filed July 22, 1947 14'sheets-sheet 14 PIER BAKKER ATTYS Patented Oct. 14, 1952 UNI'IEDvv STAT Vraum: CIRCUIT armaron Pierakker, Chicago, Ill., assigner to Automatic Electric Laboratories, Inc.,` Chicago, Ill., a corporation of Delaware Original application July 22, 1947,L Serial No.

Divided and this application January 7,1950, serial No. 137,303

' 6 Claims. 1 The present invention relates to `telephone systems and more particularly to community automatic exchange (C. A. Xl networks. This application is a division of the copending application of Pier Bakker, Serial No. 762,715, filed July 22, 1947. v

Ina C. A. X network, there is frequently provided a toll office yincluding a switchboard, a tandem oilice of the automatic type, and a suboffice .of the automatic type; whereby traic between the switchboard in the toll olce and the subscriber substations in the sub-oflice must be trunked through the tandem oiice. Also the tandem oiice frequently comprises restricted service features preventing some of the subscribersubstations therein from completing'connections directly to subscriber substations in the sub-cnice, without the aid ofl the operator at the switchboard in the toll olice.'4

It is a general object of the presentinvention to provide in a C. A. X 'networkvof the character Another object of the invention is` to provide I in a telephone system `of the type noted, an improved trunl: selector-digit sender and repeatertrunk selector arrangement in which `iirst automatic switching apparatus is responsive to a given digit to select either the repeater-trunk vselector or the trunk selector-digit sender depending upon traine conditions; whereupon the selected repeater-trunk selector selects an lidle trunk line extending' to the desired destination, or the selected trunk selector-digit sender selects an idle trunk eXtendingto second automatic switching apparatus and then operates the second switching apparatus to select an idle .trunk line extending to the desired destination.

A still further object of the invention is to provide in a trunk circuit, including an outgoing trunk, an answer relay, and a repeater having incoming and outgoing windings, an improved arrangement for transmitting impulses received via the incoming repeater winding over the outgoing trunk that utilizes the connection and disconnection of a winding of the answer relay across the line conductors of the outgoing trunk in multiple with the outgoing repeater winding.

Further features of the invention pertain to the particular arrangement of the circuit elements of the system, whereby the above-outlined and additional operating features thereof are attained.

Sect. 1.-Thc general arrangement of' the v telephone system The invention, both as to its organization and method or operation, together with further objects and advantages thereof, will best 4`be understood by reference to the following specifi; cation taken in connection with the accompanying drawings in which Figure 1' is a'schematic diagram of the area served by a telephone system embodying the present invention and illustrating the general arrangement 4of the apparatusincorporated in several ofthe oiiices thereof and Figs. 2 to 14, inclusive, taken together, illustrate the details of certain of the apparatus incorporated'in the telephone system, which apparatus has embodied therein thefeatures of the invention asbriefly outlined above. Specically, in order to'iorm a unied diagram, Figs. 2 to 9, inclusive, should be arrangedvertically in 'side- 4Icy-side relation from vleft to right, and Figs. 10

to 14, inclusive, should. be arranged vertically in side-by-side relation fromleft to right and disposed respectively below Figs. 5' to 9, inclusive.

More particularly, Fig. 2 illustrates the details of one of the toll line circuits incorporated inthe toll office; Figs. 2 to 4, inclusive, illustrate the details of one of the toll circuits incorporated in the tandem office; Figs. 5 and 6 illustrate the details of the repeater and trunk selector incorporated in the tandernofce; Figs. 10 and 11 `illustrate ther details of one of the trunk circuits a tandem oinc'e 3@` and a sub-office lllhthe'ftollv ofce l0 being disposed `relatively remote from the tandem 'oiiice 3Q, and the tandem office 30 being disposed relatively near to the magneto office 2S and to the sub-cnice 40. The tolloflice Hl serves subscriber s bstations of any suitable type and comprises a manual dial switchboard 20G; while the magneto office 29 serves subscriber substations of the magneto type and comprises a manual dial switchboard 286. The tandem ofce 3i) is a relatively small oce of the automatic type, serving a number of diierent groups of subscriber substations rendering different classes of service and at least one groupof paystations. One of the groups of subscriber substatons includes the subscriber substation TI. Also, the sub-office 40 is a relatively small oilice of the automatic type serving a group of subscriber substations,l including the subscriber substation T2.

The toll oice I and the tandem oiiice 30 are interconnected by a small group of toll lines; which group may comprise three individual toll lines, including the toll line 220. The magneto oiiice and the tandem oiiice 30,are interconnected by a small group of trunk lines; which group may comprise three individual trunk lines, including the trunk line 280. The tandem oilice and the sub-oce 40 are interconnected by a single trunk line 600; and also by a small group of trunks; which group may comprise two'individual trunks, including the trunk I |90. Each of 'the toll lines 220, etc., terminates in toll line circuits respectively disposed in the toll oice I 0 in the tandem oiiice 30, the toll line 220 terminating in the toll line circuits 2|0 and 250 respectively disposed in the toll oflice I0 and in the tandem office 30. Each of the trunk lines 280, etc., terminates in trunk line circuits respectively disposed in the magneto oiiice 20 and in the tandem oice 30, the trunk line 280 terminating in the trunk line circuits 285 and 28| respectively disposed in the magneto office 20 and in the tandem office 30. The trunk line 600 terminates in a repeater and trunk selector 500 disposed in the tandem office 30 and in a trunk line circuit 100 disposed in the sub-oiice 40. Finally, each of the trunks H90, etc., terminates in trunk circuits respectively disposed in the -tandem office 30 and in the sub-office 40, the trunk I I 90 terminating inthe trunk circuits |000 and |200 respectively disposed in the tandem oftlce 30 and in the sub-cnice 40. In the toll oflice I0, each of the toll line circuits 2|0, etc., is accessible to the switchboard 200; and in the magneto oiice 20,.each of the trunk line circuits 285, etc., is accessible to the switchboard 286.

The tandem oiiice 30 also comprises automatic switching apparatus including a plurality of finder-connector links 380, etc., provided with an associated distributor 388, and two incoming connectors 300, etc., respectively individually associated with the trunk circuits |000 etc., the

4trunk circuit |000 being connected to the individually associated incoming connector 300 by a trunk H80. Each toll line circuit 250, etc., is provided with a line circuit individual thereto, the toll line circuit 250 being provided with the line circuit 384 individually connected thereto by the trunk 380. Also each trunk line circuit 28|, etc., is provided with a line circuit individual thereto, the trunk line circuit 28| being provided with the line circuit 385 individually connected thereto by the trunk 283. Finally, each subscriber substation is provided with a line circuit individual thereto connected to the associated subscriber line, the subscriber substation TI being provided with the line circuit 381 individually connected to the associated subscriber line 386. The various line circuits 384, 385, 381, etc., are respectively connected to the distributor 388 and are accessible to the nders of the various links 390, etc. Each toll line circuit 250, etc., is provided with two incoming trunks, the toll line circuit 250 being provided with the two incoming trunks 410 and 480; and each trunk line circuit 28| etc., is provided with an incoming trunk, the trunk line circuit 28| being provided with the incoming trunk 39|. Also the repeater and trunk selector 500 is provided with an incoming trunk 490; and each of the trunk circuits |000, etc., is provided with an incoming trunk, the trunk circuit I000 being provided with the incoming trunk 400. The incoming trunks 480, etc., extending to the toll line circuits 250, etc., are accessible to the repeater and trunk selector 500 and to the two incoming connectors 300, etc; while the trunks 410, etc., extending to the toll line circuits 250, etc., are accessible to the connectors of the various links 390, etc. The incoming trunks 39|, etc., extending to the trunk line circuits 28|, etc. are accessible both to the connectors of the links 390, etc., and to the two incoming connectors 300, etc. The various subscriber lines 388, etc., are accessible to the connectors of the various links 390, etc., and to the two incoming connectors 300, etc. The incoming trunk 490 extending to the repeater and trunk selector 500 is accessible to the connectors of the various links 390, etc.; while the incoming trunks 400, etc., extending to the trunk circuits |000, etc. are accessible to the conectors of the various links 390, etc.

The sub-cnice 40 comprises automatic switching aparatus, including a plurality of finderconnector links 884, etc., provided with an associated distributor 883; and an incoming connector 885 individually associated with the trunk line circuit and connected thereto by the trunk 800. Each trunk circuit |200, etc., is provided with a line circuit individual thereto. the trunk circuit |200 being provided with the line circuit individually connected thereto by the trunk |280. Each subscriber substation is provided with a line circuit individual thereto connected to the associated subscriber line, the subscriber substation T2 being provided with the line :circuit 882 individually connected to the associated subscriber line 88|. The various line circuits 110, 882, etc., are respectively connected to the distributor 883 and are accessible to the finders of the various links 884, etc. Each trunk circuit |200, etc., is provided with an incoming trunk, the trunk circuit |200 being provided with the incoming trunk |380; and the trunk line circuit 100 is provided with an incoming trunk 910. Also the sub-ofce 40 comprises a trunk selector and digit sender |400 provided with an incoming trunk 890. The incoming trunks |380, 910, 890, etc., are accessible to the connectors of the various links 884, etc.; while the trunk selector and digit sender |400 has access to the incoming trunks |380, etc., extending to the trunk circuits |200, etc. Finally, both the connectors of the various links 884, etc., and the incoming con nector 885 have access to the various subscriber lines 88|, etc.

Sect. 2.-The apparatus incorporated in. the

telephone system In the toll oce I0, the switchboard 200 is of the conventional manual dial type, including cord circuits, not shown. Each of the toll line circuits is identical to the toll line circuit 2|0; which comprises, as shown in Fig. 2, a relay group including a simplex pulse relay R2|0 and a signal relay R2 I 5, as well as a repeating coil RC2| 1.

In the magneto oice 20, the switchboard 288 is of the conventional manual dial type and may be identical to the switchboard 200. Similarly, the trunk line circuits 285, etc., may be identical to the toll line circuit 2 I0.

In the tandem cnice, the toll line circuits 250,

etc., and the trunk line circuits 28|, etc., may be identical; the toll linecircu'it 250 comprises, as shown in Figs. 2, 3 and iii, a repeating coil RC223, a timer-425,' anda relay group including a signal 'relay R230, supervisory relay R240, a dial relay R250, a pulse relay R200, an answer relay R210, a switch relay R310, a control relay R320, a ,line relay R300, a time release relay R340, two

hold relays E350-and R300, a time release relay R310, a line relay R410, a timer-relay R420, a seize rrelayRLlSil, a tone relay R440, two start relays R445 and R450 and a reversebattery relay R400.

The repeater and trunk selector 500 comprises, as shown in Fig's. 5 and 6, a repeating coil RC600 and a relay group including three select relays R510, R520 andr R530, a reverse battery relay R540, va busy relay R550, a test relay R500, a release relay R510, a control relay R580, a line relay R500, ahold relay R010, a dial relay R020, a cut-off relay R030, an answer relay R040, a supervisory relay R050, a start select relay R055, a simplex relay R000, a ring-down relay R605 and two'startrelays R010 and R000.

The trunk circuits 1000, etc., are identical; and .the trunk circuit vv1000 comprisesjae shown in Figs. l-.O and ll, la repeating coil RC1115, a timer, not shown,and a relay group including a reverse battery relay R1010, av cut-oli` relay Rllliii,A a timer relay R1030, a seize'relay R1040, a control relay RI050, a dial relay R1060, a hold relayrR1010, two line relays R100() and R1110, a supervisory relay R1 |20, 'a time release relay R1130, an'answer relay R1140, a switch relay R1150, a hold relay R1100, and a simplex relay R1 110. i

Also, 4in the tandem office 30, the line circuits 384, 305 and 331 may be of any suitable types, while the distributor 380 is of any conventional type.v Ikhe subscriber substations TI, etc., are provided lwith conventional substation equipment;` and the paystations, not shown, are of the conventional prepayment type. Further, the private subscriber lines are provided with call registers and meters, not shown. Finally, the finder-connector links 300, etc., are of the Strowger restricted service type disclosed in the (zo-pendingapplicationrof Pier Bakker, Serial No. 123,525, rlled January 22, 1947; while each of the 4incoming connectors 000, etc., is of the Strowger type andis substantiallyidentical to' the connector' portion of the link 300. In passing, it is noted that the link 300 lis ofthe mixed service type and is responsive to the single digits 7, 8,

-9 andv 0,'respectively, to select the groups of. trunks terminated in the iirst, second, third and.

fourth levels thereof and then automatically to operate in order to select an idle trunk in .the

previously selected group or level. Also the link 390 is responsive to the prefix digits 2 or 3 followed by one of the digits 5, 6, 1, 8` and 9 to select the respectively corresponding fth, sixth, seventh, .eighth and ninth levels thereof, Aterminating the lines extending to the subscriber sub- Also the link 390 comprises a restricted service.`

arrangement, whereby certain of 'the subscriber lines may not extend connections via thev two.

groups of trunks that are respectively selected in' response to dialing the vdigits '7 and 9; andrione` of the subscriber llines may extend connections via the 'trunks that areiselected in response to dialing the digit 8.

In the sub-office .40, :the trunk line circuit comprises, as shown in Figs. '7, 8 and 9, a repeating coil RC100, a timer 030 and a relay group 1including two ring-down relays Rv and R120, a switch relay R130, a 'line relayzR140, an answer relay R150, a hold relay R810, a simplex relay R320, a hold relay R830, a time release'relay R840, a dial relay R850, a control relay R800, a line relay R810, a tone relay R910, a seize relay R920, two start relays 'R930 and R040, a. timer relay R050 and a reverse battery relay R960.

Also, the trunk circuits 1200, etc., are identical to the trunk circuit 1000; the trunk circuit 1200 comprising, as shown in Figs. 12 and 13, a repeating coil RC1215, a timer, not shown, and a relay group including a reverse battery relay R1310, a cut-off relay R1320, a timer relay R1330, a seize relay RI300, a control relay RI350, a dial relay R1300, a hold relay R1310, two line relays R1380 and R1210, a supervisory relay R1220, a time release relay R1230, an answer relay R1240, a switch relay R`I250, a hold .relay R1200 and simplex relayRI210.

Also in the sub-office 40, the line circuits '110, 802, etc., may be oi any suitable types; While the distributor 083 is of any conventional type. The subscriber substations T2, etc., are provided With conventional substation equipment; while links 804,etc., and the incoming connector 085, are of the conventional Strowger types.

Finally, the trunk selector and digit sender 1400 comprises, as shown in Fig. r14, a relay group including two select relays R1410 and R1420, a busy relay R1`430, a test relay R1440,'a cut-oil` relay R1450, three pulse relays R1485, R1455, and R1460, a shunt relay Rl410, a'line relay'Rl415ya control relayRM), and a start relay R1490. Also., the trunk selector and digit sender '|400 comprises a send switch 1401 ofthe rotary type, including two wipers 1402 and 1403 providedwith a Vmagnet M1404 for driving the wipers noted step-by-step in the clockwise direction away from their home positions with respect to the associated contact banks.

- A better understanding of the connection and arrangement `of the apparatus -incorporated in thetelephone system will be facilitated from a consideration of the extension of calls involving the various ofces. y

Sect. .SL-Local calls in the tandem ofce First-assuming that a call is initiated at the ,subscriber substation T1 in the tandem oice 30 that `is to be completed locally to another subscriber .substation therein, the line circuit 381 .is controlled via the subscriber line 3.80m rorder .to govern operation of the distributor 380; whereby an idle one of the links, such, for example, as the link .-1190 is assigned thereby. 'The finder oi the assigned link 000 .operates to iind the subscriber line 380 extending to the calling subfscriber substation T1; whereby the line circuit 381 is operated in order to mark the subscriber line 306 as busy to the other links `300, etc. Also the connector of 'the link 390 operates to return 7 dial tone over the subscriber line 38B to the calling subscriber substation TI; whereby thesubscriber at the calling subscriber substation T| proceeds to dial the directory number of the called subscriber substation, which number might be 3654. The first digit 3 received by the link 300 indicates that the present call is a local call and selects a portion of the ringing code. The connector of the link 390 responds to the second digit 6 to select the corresponding sixth level; and then responds to the third digit to select the corresponding fth line in the previously selected level; which line extends to the called subscriber substation.| The connector of the link 390 then responds to the fourth digit 4 to select the remainder of vthe ringing code that is to be employed to ring the called subscriber line. The ilrst or prefix digit 3,in conjunction with the fourth digit 4, selects one of twenty ringing codes at this time; whereby the particular selected ringing code is projected over the called subscriber line in order to signal the corresponding one of the twenty party subscriber substations connected to the called subscriber line, assuming the called subscriber line is of the twenty party type and provided it is idle at this time. The operation of the connector of the link 390 to return busy tone current to the calling subscriber substation T in the event the called subscriber line is busy is in accordance with conventional practice; and the remainder of the operation of the connector of the link 390 in response to the answering of the call on the called subscriber line, as well as the subsequent release of the established connection, are in accordance with conventional practice.

In view of the foregoing, it will be understood that a call from a subscriber substation in the tandem exchange 30 may be completed locally to a paystation therein in an identical manner.

Also, it will be understood that a call may be initiated at a paystation in the tandem exchange 30 by depositing a coin or check thereat and then subsequently completed locally to a called subscriber substation or paystation therein ina conventional manner.

Sect. 4-A call ,from a subscriber substation or a paystation in the tandem office to a subscriber substation in the sub-o17ce First assuming that a call is to be extended from a subscriber substation, such, for example, as the subscriber substation TI in the tandem oiiice 30 to a called subscriber substation, such,

for example, as the subscriber substation T2 in the subfoice 40, the subscriber at the calling subscriber substation T| iirst initiates the call; whereby the link 390 may be taken for use in the manner previously explained. The subscriber at the calling subscriber substation TI then dials by the absence of ground potential upon the con- 5 trol conductor C403 thereof. When the connector of the link 390 seizes the trunk 400, a loop circuit is completed for energizing in series the windings of the line relays R|080 and Rl I |0 in the trunk circuit |000; this loop circuit extending from ground potential by way of the winding of Athe line relay RI080, the contacts ||54, the lower left-hand winding of the repeating coil RCI |15 and the contactsv I 0|4 to the line conductor C402 of the trunk 400, and from battery potential by way of the winding of the line relay RI I I0, the contacts I |52, the upper left-hand winding of the repeating coil RCI |15 and the contacts |0|2 to the line conductor C| of the trunk 400. rAt this time the line conductors C40| and C402 of the trunk 400 are connected together by way of the link 390 and the subscriber line 386 at the calling subscriber subst-ation TI. When this loop circuit is thus completed, both of the line relays R|080 and RI I0 operate. Upon operating, the line relay Rl I l0 completes, at the contacts I|||, a circuit for operating the hold relay R|010. Upon operating, the hold relay R|010 completes at the contacts |013, a path, including the contacts I I |3, for 1applying batterypotential by way of the winding of the supervisory relay R||20 to the simplex conductor C| |16; which simplex conductor CI |16 is connected by way of the upper and lower right-hand windings of the repeating coil RC||15, the line conductors of the trunk and the upper and lower left-hand windings of the repeating coil RCI215 to the simplex conductor C|216; which simplex conductor C|216 is connected by way of the contacts |314 and |353 and the winding of the simplex relay R|210 in the trunk circuit |200 to ground potential. Accordingly, at this time the winding of the supervisory relay RI |20 in the trunk circuit |000 is energized in series with the winding 0f the simplex relay R|210 in the trunk circuit |200; whereby both the supervisory relay RI |20 and the simplex relay R|210 operate. Also upon operating, the hold relay R|010 in the trunk circuit |000 completes, at the contacts |012, a circuit including the contacts |034, for operating the time release relay R||30. Upon operating, the time release relay Rl |30 completes, at the contacts II34, a path for applying ground potential to the control conductor C403 ofthe trunk 400, thereby to mark the trunk 400 as busy to the other links. 390 etc., having access thereto. Also the time release relay R|I30 completes, at the contacts |35, a path for applying ground potential to the timer start conductor CI |38 in order to initiate operation of the associated timer, not shown. Further the time release relay RI |30 completes, at the contacts I |31, a path, including the contacts |02| and |032, for applying battery potential by way of the winding of the timer relay R|030 to the timer conductor Cl024; however, the timer relay RI030 is not operated at this time.-

Upon operating the simplex relay R|210 in the trunk circuit |200 completes, at the contacts |213, a circuit for operating the hold relay RI 260. Upon operating, the hold relay RI260 completes, at the contacts |262, a circuit for operating the switch relay R|250 and a multiple circuit vfor energizing the lower winding of the answer relay Rl240. When the lower winding of the answer relay R|240 is thus energized, it does not operate at this time. Upon operating the switch relay R|250 interrupts, at the contacts |252 and |254, normal connections between the windings of the line relays RI2 |0 and R|360 and the upper righthand winding and the lower right-hand winding, respectively, of the repeating coil RCI 215; and completes, at the contacts |25|, |253, |255 and |256, a path, including the resistor |224 and the upper right-hand winding and the lower right-hand winding of thelrepeating coil RCI215, for bridging the upper 'winding of the answer relay RI2l|0l across the line conductors CI28| and C|282 of the trunk |280 extending to theline circuit 110. Further, the switch relay R|250 completes, at the contacts 1250,a path, including the contacts |233. for applying ground potential to the control conductor C|3B3 of the trunk |380, thereby to mark the trunk |380 as busy to the various links 884, etc., having access thereto.

When the upper winding of theanswer relay R|240 is-thus bridged across the line conductors C| 28| and C1282 of the trunk |280, it is energized, but it is not poled to operate. Also, the line circuit operates to control the distributor 883; whereby an idle one of the nder-connector links, such, for example, as the link 880 is assigned for use at this time. Thennder of the link 880 nds the calling trunk |280 marked yby theline circuit 110; whereby the connector of the link 884 is conditioned to beresponsive to digits. received over the trunk-l280.

When the subscriber at thecalling subscriber substation TI dials the iirst digit 2 of the directory number of the called subscriber substation T2, the` line relays R|080 and Rl I 0 in the trunk circuit |000V follow. Each time the line relay Rl I I0 restores and then reoperates, it interrupts and. then recompletes, at the contacts ||II, the

`previously mentioned circuit for .maintaining operated the hold relay RIO'I0; whereby the latter relay remains operated during impulsing as it is of the slow-tc-release type'. Also each time the line relay RI I |0 restores and then reoperates, it completes and then interruptsat the contacts III2, a circuit, including the contactsv |022 and I'I32, for operating the dial relay R|0B0; whereby the latter relay operates Vand remains operated during impulsing as it. is of the slow-to-release type. Upon operating, the dial relay R|060 completes, at the contacts |003, a path, including the contactsv |01I, for connecting the resistor |025 in, shunt to the winding of the line relay R|`080 in order to improve impulsing` over the loop circuit` extending, back to the calling subscriber substation TI.` Also the dial relay R|060 completes, at the contacts |005, av path, including the c ontacts H30, for` connecting the resistor I'I25in shunt to the winding ofv the supervisory relay R|I in. order to improve impulsing overthe in series the winding of the. supervisory relay .l

RI |20 in thetrunk circuit |000 and the winding of the simplex relay R'I210 in the trunk circuit |200; whereby the relays mentionedfollow; following by the supervisory relay RI|20 in the trunk circuit |000 being without'eiiect.

y The rst time the simplexrelayVRI2`|0 in the trunk circuit |200 restores and then reoperates,y it completes andY then interrupts, at the contacts |212', ay circuit, includingV the contacts |264, |263 and |343, for energizing in series lthe upper and lower windings of, the seize relay R|3401; whereby the latter relay operates.- Upon operating the seize relay R|340 completes, at the contacts |342,I a holding circuit, including the contacts |258 and the grounded control conductors C1283 ofy the trunk |280, for energizing in series the upper and. lower windings thereof. Also each time the simplex relay R|2`|0 restores and then reoperates, it interrupts and then recompletes,v at the contacts |213, the previously l0 mentioned circuit for maintaining operated the lhold relay M250; whereby the latter relay remains operated during impulsing as it is of the slow-to-release type. Also, each time the simplex relay R|2l|0 restores and then reoperatesfit completes and then interrupts, at the contacts |212, a circuit, including the contacts |264 and |24I, for operating the dial relayRlSS; whereby the latter relay operates and remains oper ated during impulsing as it is of the slow-torelease type. Upon operating the dial relay RI3|50 completes, at'the contacts |36I, a path, including the resistor |223 and the contacts I20I, |2`|| and |25I, across the line conductors C|28| and CI202 of the trunk |200; thereby to improve impulsing over the trunk |230 and the line circuit 170 to the connector` of the link 880. Finally, each time the simplex relay RI210 restores and then reoperates, it interrupts andthen recompletes, at the contacts |27 I, the previously traced path across the line conductors C|28| andnCI282 of the trunk |280; whereby the impulses of the second digit 2 are transmitted over the trunk |280 and the line circuit 'li)` to the connector t of the link 061iA in order to effect corresponding operation thereof.

At the conclusion of the second digit 2v dialed at the calling subscriber substation Ti, 'the line relays RI080 and Ri I |0 in the trunk circuit |000 remain operated; whereby the hold relay 'RI010 is retained in its operated position and shortly thereafter the dial relay RI030 restores. Upon restoring the dial relay Rl removes the resistors |025 and I|25 from across the 'winding of the line relay R|080 and the winding of the supervisory relay RI |20, respectively. rAlsofat this time the winding of the supervisory'relay RI |20 in the trunk circuit |000A and the'winding ofthe simplex relay RI2'I0 in thetrunk circuit I200 are steadily energized in series circuit relation; whereby the relays mentioned are retained in their operated positions, ,A

The operated simplex relay R|270 in the trunk circuit |200 retains operatedthe hold relaysRI 260 andeiects restoration of the dial relay R|300 shortly thereafter, since tl1e `latter, relay islof the slow-to-release type.` Upon `restoring"the dial' relay Rl3t0interrupts, at' the contacts 136|, the previously traced path for connectingr the resistorV |223 across the vline conductors' C|2`8| and c1282 of the ,trunk 12st; whereby the upper winding of the lanswer relay `R|240`is no'longer short-circuited by the resistor |223;4 DAlso yupon restoring, the dialv relay RI360 completes, at the contacts |304, a holding circuit, includingthe contacts |342, I30I, |251 and |262, for energizing in series the upper and lowerA windings of the seize relay H5300; and a multiple" path, also .including theicontacts |258, for applying ground potential in the trunkci'rcuit |200 to the' control conductor CI283 of the trunk |280,v thereby -to retain operated the link. 884..

In view ofthe foregoing explanation otith'e manner in which thesecond digit 2' dialed attire calling subscriber substation Ti is received by the trunkV circuit |000V and repeated therefrom over the trunk. H to the. trunk circuit n[-200 and then repeated therefrom to the connector of the link 804,. it will be understood thatthe third digit 3 dialedv at the calling subscriber substation TI is transmitted in an identical-manner tothe connector of theflinkv 084'. The connector of the link 804 responds to the digits '.2 and?,v to select the subscriber line 88| extending lto the calledsubscriber. substation T2. The sub,-

11 @quent foperation of the connector of the link '884 depends upon the idle or'busy condition of the called subscriber substation T2 at this time; and in the event the called subscriber substaition T2 lis'busy at this time, the "connector of ythe link 884 operates in order to return busy tone current over the trunk |280 to the trunk cir- `'cuit If'2u0'.; 'which "busy tone current vlt'rzfiversirig the upper right-hand winding and the lower right-hand winding of the repeating coil RCI'2'I5 induces 'a corresponding b'usy tone current in 'the left-hand windings thereof. The busy tone lcurrent is returned over the trunk I |90 and trav- 'ersing the right-hand windings of the repeating coil RCII'I5 induces a corresponding busy 'tone current in the upper left-hand winding andthe lower left-hand winding thereof; which fbusytone current is returned over the loop cirfcuit to the calling subscriber substation TI in order to indicate to the subscriber thereat that the desired connection cannot be had at this time by virtue of the busy condition of the called subscriber substation T2.

On the other hand, in the event the called subscriber substation T2 is idle at this time, ringing current is projected from the connector of the link 884 over the subscriber line 88| thereto and the line circuit 882 is operated in order to mark the subscriber line 88| as busy to the other links 884, etc., having access thereto. Also, ring-back tone current is returned from the connector f the link 884 over the previously traced connection to the calling subscriber substation `TI in order to indicate to the subscriber thereat that the called subscriber substation T2 is being rung.

When the subscriber at the called subscriber substation T2 answers the call, the connector of the link 884 operates in order to reverse the polarity of the trunk |280; whereby the upper winding of the answer relay'RI240 is poled to operate. Upon operating, the answer relay RI 240 completes, at the contacts |242, a circuit for energizing the upper winding of the control relay R|350; whereby the latter relay operates. Upon operating the control relay RI350 completes, at the contacts |354 a holding circuit, including the contacts |222 and |250 and the resistor |225, for energizing the winding of the simplex relay RI210; interrupts, at the contacts |353, the previously traced original path for connecting ground potential by way of the winding of the simplex relay RI 210 to the simplex conductor C|216; and completes, at the contacts |352, a path, including the contacts |314 for connecting battery potential by way of the winding of the supervisory relay RI220 to the simplex conductor CIZ'II. Accordingly, at this time the winding of the supervisory relay R|220 in the trunk circuit |200 is short-circuited in series with the winding of the supervisory relay RII in the trunk circuit |000; whereby the supervisory relay RI220 is retained in its restored position and the supervisory relay RI |20 restores.

Upon restoring, the supervisory relay RI |20 in the trunk circuit |000 completes, at the contacts I|2I, a circuit, including the contacts IU'II, |062 and II3I, for energizing the winding of the cutoi relay RI220, and a multiple circuit, also including the contacts I08I, for energizing the winding of the reverse battery relay RIOI0; whereby the cut-oi relay RI020 and the reverse battery relay RIOI0 operate shortly thereafter, both cf these relays being of the slow-to-operate type. Upon operating, the cut-off relay RI020 and the reverse battery relay RIOI0.

interrupts, V'at fthe contacts I0'2`I, t'he "previously traced connection between the wind-ing of the timer relay -R'I 030 andthe timer conductor C I 024, thereby posi-'tively to prevent operation of the timer relay RI030 under the rcontrol of the associated timer, not shown. Upon operating, the yreverse battery relay RIOI0 completes, at the contacts I 0I5, a holding circuit for energizing the winding thereof, and including the contacts II3I, II2f|, |062 and I01I. Also the reverse batte'ry relay`R|0I0 reverses, at the contacts IIIII, |0|2, I0|3 and |0|4, the polarity of the trunk 400 with respect to the line relays RI 080 and RI I I0; which reversal of polarity over the trunk 400 and the link 380 is effective to operate a meter, not shown, individually associated with the calling subscriber substation TI or otherwise to assess a charge against the calling subscriber substation TI. At this time an established connection is completed between the calling subscriber substation TI in the tandem office 30 and the called subscriber substation T2 in the suboil'ice 40.

At the conclusion of the established connection, when the subscriber at the called subscriber substation T2 disconnects, the connector of the link 884 is operated in order again to reverse the polarity of the trunk |280; whereby the answer relay RI240 in the trunk circuit |200 is poled to restore. Upon restoring, the answer relay RI240 interrupts, at the contacts |242, the previously mentioned circuit for energizing the upper winding of the control relay RI350, thereby to cause the latter relay to restore. Upon restoring, the control relay R|350 interrupts, at the contacts I 352, the previously traced path for connecting battery potential by way of the winding of the supervisory relay RIZZO to the simplex conductor CINE; interrupts, at the contacts |354, the previously traced holdingl circuit for maintaining operated the simplex relay RI 210; and recompletes, at the contacts |353, the previously traced original path for applying ground potential by Way of the winding of the simplex relay RI2I0 to the simplex conductor C|2`|6. Accordingly, at this time, the winding of the simplex relay RI2`I0 in the trunk circuit |200 is again energized in series with the winding of the supervisory relay RI |20 in the trunk circuit |000; whereby 'the simplex relay RI2I0 is retained in its operated position and the supervisory relay RII 20 reoperates. Upon reoperating', the supervisory relay RII20 interrupts. at the contacts ||2|, the previously traced circuits for maintaining operated the cut-01T relay RI020 Upon restoring, the reverse battery relay R|0|0 again reverses, at the contacts I0|I, I0|2, |0|3 and `IOI4, the polarity of the trunk 400 with respect to the line'relays R|080 and RI I I0 in the trunk circuit |000; however without effect at this time. Upon restoring, the cut-off relay RI 020 again completes, at the contacts |02I, the previously traced connection between the winding of the timer relay R|030 and the timer conductor CI024 extending to the timer, not shown; whereby operation of the timer is again rendered effective.

When the subscriber at the calling subscriber substation TI disconnects, the loop circuit extending to the line relays RI 080 and RII I0 in the trunk circuit I 000 is interrupted; whereby the relays mentioned restore. Upon restoring, the line relay RI I I0 interrupts, at the contacts I I I I, the previously mentioned circuit for maintaining operated the hold relay RI010; whereby 

